New to Dex/Dex accuracy

Second go with Dexcom last night. First try my receiver had to be replaced before I could get past sensor warmup. This receiver seems better but this morning I noticed that when I click the button a dark grey screen comes up like a little lag for a second before anything comes on screen. Anyone else’s do the same?

This morning my meter and Dex were off by 31 points. Just now they were off by 54. Meter said 189 Dex said 130 something. I calibrated and it says 175 right now. Is that normal to have such a big difference?

A lot of people report erratic results in the time before it fully acclimates–I think the official time is something like 24-36 hours. I have occasionally seen readings that were that far off, but generally they’re much tighter than that. There are significant metabolic changes during sleep, so it may be just a matter of it “learning” your patterns. I’d see how it does over the next 24 hours.

Haven’t seen that on mine. Is it persisting or did it just do that the one time?

A couple things to make sure you do for better accuracy or general knowlege:

  1. Calibrate during periods of steady BG.
  2. Calibrate when in a good BG range.
  3. Dexcom doesn’t measure BG–just interstitial fluid. There WILL be a delay in BG value vs. Dexcom value if falling or rising.

@LexaBeee To add to what Bradford posted,;
only calibrate when the dex prompts you for it (every 12 hours), over calibration leads to inaccuracy.

Also, there is a slight lag when you push the button of 1/2 a second I’ve noticed.

Though they do say to only calibrate unprompted when it varies more than 20% from fingerstick. I agree it’s best to resist the impulse to tweak–it generally does more harm than good–but 189 vs 130 is definitely outside the margin of error.


One thing I have learned, too, is not to correct it if I’ve done something that I KNOW is going to make it go outside the margin of error. Many people have reported that use in a hot tub, for instance, will give false highs. The first time it happened, I corrected it. Now I just know that I’m going to get a false high, followed by a rapid downward slope as it self-corrects and comes back into line with what my meter reading would actually be.

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The bottom line is:

Correct only when the arrow is horizontal!

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What about when it is prompting for the 12 hour calibration, do you still wait for a horizontal arrow? I know it keeps on working without the calibration, it’s just annoying to get the blood prompt every time you wake up the receiver.

I am using a Dexcom G5 with the xdrip app that is being beta tested. Let me tell you the xdrip app is way more accurate than the Dexcom receiver. Wait until the app comes out and use that instead of the Dexcom receiver.

Yes, if the arrow is not horizontal, I have my daughter wait until it is before calibrating. Waiting can be annoying, but the payoff is that her Dexcom is so scary-accurate that I trust it way more than her meter. Let’s put it this way: she is now using only two strips per day (only one if she forgets one of the two calibrations)…

I always try and calibrate when I have a horizontal arrow, even if it means dealing with the annoying prompt. I also don’t calibrate first thing in the morning because I know I experience Dawn Phenomenon, and that my Dexcom may be lagging behind it. My latest sensor has been freakishly in tune with my Accu-Chek (often within 5pts), to the point that I’ve begun to trust it to dose my insulin off of it, and I’m really only finger-sticking 2x daily.

BTW, I’m an Android user, so couldn’t use the G5. I opted to go with the G4. After I got it, I learned about the folks at Nightscout which lets me Share with my husband without needing an iPhone. An added bonus is that the xDrip display on my phone is more detailed than the simple arrows up/down than on the Dexcom receiver. I can see exactly how many points I’ve dropped between one reading and the next, and even click on previous readings over the past hour to check. Right now, for example, my Dexcom receiver says I’ve got a BG of 111 with a right-arrow. But xDrip is showing a 111 with a right arrow, but that I dropped 5 mg/dl 3 minutes ago. For me, personally, that’s still too much of a fast drop to calibrate with and I’ll usually wait until it’s only 1 or 2, 3 at the most before calibrating.

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So frustrating. It’s off by 60 now. Meter says 226 and Dex said 166 with arrow slightly upward. Literally maybe a minute later it says 164 now with steady arrow on Dex. And just now 167 with steady arrow. I don’t get it. I feel overwhelmed now! Ugh. Could it maybe be the sensor?

It could be the sensor. If you’ve had multiple way-off readings from the same sensor, it might be worth calling Dexcom and telling them what’s going on. They’ll replace faulty sensors.

Try a different site maybe. There is definitely something wrong. I have noticed that if it gets snagged on something–it could pull out slightly (but enough to cause problems in accuracy).

I’m also using xdrip beta with g5 and also found it to be more accurate than the receiver, too. Although xdrip cannot be used simultaneously with the receiver unlike with the iPhone software, apparently, so I now only use xdrip. Right now I’m having the same problem though with inconsistencies between the sensor and xdrip. I’m not sure why. Maybe simply because it is a new sensor, only two days old. I’ve been calibrating the xdrip several times now to try to get it back on track…

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I have noticed that it is is quicker than dexcom receiver to adapt to new sensor. I always hated you had to waste a day and a half to get some accuracy from a new sensor with a Dexcom receiver.

Just woke up a little while ago. Checked my sugar on fasting was 178 Dex said 156 so about 23 points off. I’ll wait it out until tonight & call if it continues to be off so much. How many points off is normal for your meter and Dex to be by? Is Dex supposed to be more accurate than finger sticks? I think what’s so frustrating is that even on different fingers and strips the numbers are so different you don’t ever know what it really is.

What is xdrip? Can I use that on my iPhone?

Fingersticks are presumed to be more accurate, though the FDA requirements for glucose meters are something like ±20% (about which there is much complaining and gnashing of teeth around here), and some machines are reputedly more accurate than others. Bayer Contour Next+ is reputed to be very good, though not the only good choice. A whole topic of its own, obviously.

Mine is usually within 20, most frequently within 10, and just recently it’s regularly been within like 5 (maybe I just have a really good sensor in a really good location*). So no, I don’t think the numbers should regularly be as far off as what you’re seeing. I’d go ahead and call Dexcom.

*Note that this is another factor that can make a difference. Belly is the only location officially recommended by the manufacturer but it’s by no means the only one people use. A lot of us find the back of the upper arm more convenient and more accurate compared to fingersticks. There are videos about how to insert one there–it’s a little awkward but doable even single-handed.